1. Field of the Invention
The invention relates to an assembly for ignition of gas turbine combustors. In addition, this invention relates to devices for continuous stabilization/re-ignition of lean low NO.sub.x combustion. This invention also relates to igniters for use in place of conventional spark plug fuel ignition systems.
2. Brief Description of Related Art
Commercial aircraft gas turbine combustors utilize combustor wall mounted igniters, typically a spark plug, for combustor light-off. This requires the presence of fuel close to the wall. Inasmuch as combustion of fuel near the wall during full power operation tends to raise the wall temperature, combustor designs tend to be a compromise between ignition and operational requirements. Thus there have been numerous attempts to achieve ignition away from the wall. Ideally, ignition should be achieved right at the fuel source so that ignition of the initial fuel flow is possible. This avoids the necessity to dump unburned fuel into the combustor prior to ignition (creating the potential for hot starts or explosive detonations with consequent damage to the turbine) and enables the use of spray patterns which keep fuel away from the combustor walls.
Accordingly, there has been interest in integrating the ignition source into the fuel injector. For example, U.S. Pat. No. 4,938,019 describes a fuel nozzle with an integrated spark plug igniter assembly and U.S. Pat. No. 4,825,658 describes a fuel nozzle with a catalytic glow plug igniter assembly. Such designs have major drawbacks which limit utility. For example, a spark plug integrated into an injector is subject to fouling if wetted by liquid turbine fuel, rendering it inoperative. In addition, size limitations reduce spark plug life. On the other hand, although the glow plug of U.S. Pat. No. 4,825,658 eliminates the fouling problem of spark plugs, the glow plug is designed such that the return flow of the recirculating flow downstream of the injector contacts the hot glow plug surface resulting in ignition of the downstream recirculating gases. Inasmuch as the initial direction of the incoming fuel-air flow from the swirler is away from the glow plug considerable fuel can travel downstream before sufficient fuel is injected to increase the recirculation zone fuel concentration high enough at the glow plug to allow ignition. Thus explosive detonation is possible as is the case with conventional spark igniters presently used in aircraft gas turbine engines. Advantageously, fuel should be ignited immediately as it enters the combustor.
In the present invention atomized fuel entering a gas turbine combustor is reliably ignited as it enters the combustor by contact with a continuous pilot flame projected into the combustor distal to the combustor walls, at a location to ignite the incoming fuel. The present invention offers the advantages of away-from-the-wall ignition coupled with continuous flame stabilization by providing for projection of the pilot flame into a combustor, whether from the liner wall or from the combustor centerline.